1. Field of the Invention
The invention relates to a sensor circuit for correlated double signal sampling, the sensor circuit comprising a sensor device having an output for supplying a sensor output signal, a sampling circuit coupled thereto for performing the sampling operation, and a clock pulse generator which is coupled to the sensor device and the sampling circuit for applying multi-phase control clock pulse signals thereto.
2. Description of the Related Art
A sensor circuit of this type is known from an Article in the journal "IEEE Journal of Solid-State Circuits" of Feb. 1974, pp. 1 to 12. The sensor device suitable for picture pick-up is described as a charge-coupled device which is a specific implementation of a charge transfer device for generating a picture signal as the sensor output signal. To obtain an improved picture quality upon display, the correlated double signal sampling operation is performed during pixel periods. The double signal sampling implies that during a pixel period, firstly the signal is clamped on a reference voltage level via a series capacitor, whereafter the actual signal sampling operation is performed with a storage of samples in a capacitor. In this way, as described, noise produced by a reset switch is removed, switching transients are eliminated and low-frequency noise is suppressed. A two-phase control is described of a parallel-in, series-out sensor output register for supplying the sensor output signal and of the sampling circuit operating with two series of sampling pulses.
In current sensor devices, the time difference between taking the two samples per pixel period is smaller or is of the order of 100 ns. This imposes strict requirements on the accuracy with which the sampling clock pulses are generated by the clock pulse generator. Consequently, the components of the clock pulse generator must not have a large spread in signal delay times and should remain stable in time. A complicated and expensive clock pulse generator must be used in the sensor circuit.